Proteins and DNA related to salt tolerance in plants

ABSTRACT

The present invention relates to proteins and nucleic acids related to salt tolerance in plants.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit to U.S. provisional application No. 60/194,648, filed on Apr. 4, 2000, and incorporated herein by reference in its entirety.

STATEMENT OF FEDERALLY FUNDED RESEARCH

[0002] This invention was supported by the National Institutes of Health by Contract No. R01GM59138. The government may have certain rights to this invention.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention relates to proteins and nucleic acids related to salt tolerance in plants.

[0005] 2. Description of the Background

[0006] Soil salinity is a major abiotic stress for plant agriculture. Sodium ions in saline soils are toxic to plants due to its adverse effects on K⁺ nutrition, cytosolic enzyme activities, photosynthesis and metabolism (1, 2). Three mechanisms function cooperatively to prevent the accumulation of Na⁺ in the cytoplasm, i.e. restriction of Na⁺ influx, active Na⁺ efflux and compartmentation of Na⁺ in the vacuole (1). The wheat high-affinity K⁺ transporter HKT1 functions as a Na⁺-K⁺ cotransporter, which confers low-affinity Na⁺ uptake at toxic Na⁺ concentrations (3). Thus HKTI could represent one of the Na⁺ uptake pathways in plant roots. The low-affinity cation transporter LCT1 from wheat may also mediate Na⁺ influx into plant cells (4). In addition, patch clamp studies have shown that non-selective cation channels play important roles in mediating Na⁺ entry into plants (5). The Arabidopsis thaliana AtNHX1 gene encodes a tonoplast Na⁺/H⁺ antiporter and functions in compartmentalizing Na⁺ into the vacuole (6). Over-expression of AtNHX1 enhances the salt tolerance of Arabidopsis plants (7).

[0007] No Na⁺ efflux transporter has been cloned from plants. Plants do not appear to have a Na⁺-ATPase at the plasma membrane (1). It is expected that proton motive force created by H⁺-ATPases would drive Na⁺ efflux from plant cells through plasma membrane Na⁺/H+antiporters (8). Fungal cells contain both Na⁺-ATPases and Na⁺/H⁺ antiporters at the plasma membrane. In the yeast Saccharomyces cerevisiae, plasma membrane Na⁺′-ATPases play a predominant role in Na⁺ efflux and salt tolerance (9). In contrast, Na⁺/H⁺ antiporters are more important for Na⁺ efflux and salt tolerance in the fungus Schizosaccharomyces pombe (10).

[0008] Recently, several Arabidopsis sos (for salt overly sensitive) mutants defective in salt tolerance were characterized (11, 12, 13). The sos mutants are specifically hypersensitive to high external Na⁺ or Li⁺ and also unable to grow under very low external K⁺ concentrations (13). Allelic tests indicated that the sos mutants define three SOS loci, i.e., SOS1, SOS2 and SOS3 (13). The SOS3 gene encodes an EF-hand type calcium-binding protein with similarities to animal neuronal calcium sensors and the yeast calcineurin B subunit (14). In yeast, calcineurin plays a central role in the regulation of Na+ and K⁺ transport. Mutations in calcineurin B lead to increased sensitivity of yeast cells to growth inhibition by Na+ and Li⁺ stresses (15). The SOS2 gene was recently cloned and shown to encode a serine/threonine type protein kinase (16). Interestingly, 5052 physically interacts with and is activated by SOS3 (17). Therefore, SOS2 and 5053 define a novel regulatory pathway for Na⁺ and K⁺ homeostasis and salt tolerance in plants. The SOS3/SOS2 pathway has been predicted to control the expression and/or activity of ion transporters (17). However, the identities of the transporters regulated by this pathway are not known.

[0009] Among the three SOS loci, SOS1 plays the greatest role in plant salt tolerance.

[0010] Compared to sos2 and sos3 mutant plants, sos1 mutant plants are even more sensitive to Na⁺ and Li⁺ stresses (13). Double mutant analysis indicated that SOS1 functions in the same pathway as SOS2 and SOS3 (12, 13). Thus, SOS1 may be a target for regulation by the SOS3/SOS2 pathway.

[0011] Accordingly, there remains a need in the art to isolate the SOS1 gene and the protein encoded thereby.

[0012] Furthermore, because of limited water supplies and the widespread use of irrigation, the soils of many cultivated areas have become increasingly salinized. In particular, modern agricultural practices such as irrigation impart increasing salt concentrations when the available irrigation water evaporates and leaves previously dissolved salts behind. As a result, the development of salt tolerant cultivars of agronomically important crops has become important in many parts of the world. For example, in salty soil found in areas such as Southern California, Arizona, New Mexico and Texas.

[0013] Dissolved salts in the soil increase the osmotic pressure of the solution in the soil and tend to decrease the rate at which water from the soil will enter the roots. If the solution in the soil becomes too saturated with dissolved salts, the water may actually be withdrawn from the plant roots. Thus the plants slowly starve though the supply of water and dissolved nutrients may be more than ample. Also, elements such as sodium are known to be toxic to plants when they are taken up by the plants.

[0014] Salt tolerant plants can facilitate use of marginal areas for crop production, or allow a wider range of sources of irrigation water. Traditional plant breeding methods have, thus far, not yielded substantial improvements in salt tolerance and growth of crop plants. In addition, such methods require long term selection and testing before new cultivars can be identified.

[0015] Accordingly, there is a need to increase salt tolerance in plants, particularly those plants which are advantageously useful as agricultural crops.

SUMMARY OF THE INVENTION

[0016] The present invention is based, in part, on the isolation of the SOSI locus through positional cloning. It is predicted to encode a transmembrane protein with similarities to plasma membrane Na⁺/H⁺ antiporters from bacteria and fungi. The results of the present invention suggest that a plasma membrane-type Na⁺/H⁺ antiporter is essential for plant salt tolerance. The steady state level of SOS1 transcript is up-regulated by NaCl stress. The sos2 mutation abolishes SOS1 up-regulation in the shoot. In the sos3 mutant, no SOS1 up-regulation is found in the shoot or root. Therefore, SOS1 gene expression under NaCl stress is controlled by the SOS3/SOS2 regulatory pathway.

[0017] Accordingly, the present invention provides an isolated polynucleotide which encodes a protein comprising the amino acid sequence of SEQ ID NO:2.

[0018] In a preferred embodiment the polypeptide has Na+/H+ transporter activity.

[0019] In another preferred embodiment the polynucleotide comprises SEQ ID NO:1, polynucleotides which are complimentary to SEQ ID NO:1, polynucleotides which are at least 70%, 80% and 90% identical to SEQ ID NO:1; or those sequence which hybridize under stringent conditions to SEQ ID NO:1, the stringent conditions comprise washing in 5×SSC at a temperature from 50 to 68° C.

[0020] In another preferred embodiment the polynucleotides of the present invention are in a vector and/or a host cell. Preferably, the polynucleotides are in a plant cell or transgenic plant. Preferably, the plant is Arabidopsis thaliania or selected from the group consisting of wheat, corn, peanut cotton, oat, and soybean plant. In a preferred embodiment, the polynucleotides are operably linked to a promoter, preferably an inducible promoter.

[0021] In another preferred embodiment the present invention provides, a process for screening for polynucleotides which encode a protein having Na+/K+ transporter activity comprising hybridizing the polynucleotide of the invention to the polynucleotide to be screened; expressing the polynucleotide to produce a protein; and detecting the presence or absence of Na+/K+ transporter activity in said protein.

[0022] In another preferred embodiment, the present invention provides a method for detecting a nucleic acid with at least 70% homology to nucleotide SEQ ID NO:1, sequences which are complimentary to SEQ ID NO:1 and/or which encode a protein having the amino acid sequence in SEQ ID NO:2 comprising contacting a nucleic acid sample with a probe or primer comprising at least 15 consecutive nucleotides of the nucleotide sequence of claim 1, or at least 15 consecutive nucleotides of the complement thereof.

[0023] In another preferred embodiment, the present invention provides a method for producing a nucleic acid with at least 70% homology to the polynucleotides of the present invention comprising contacting a nucleic acid sample with a primer comprising at least 15 consecutive nucleotides of the nucleotide sequence of claim 3, or at least 15 consecutive nucleotides of the complement thereof.

[0024] In another preferred embodiment, the present invention provides a method for making SOS2 protein, comprising culturing the host cell carrying the polynucleotides of the invention for a time and under conditions suitable for expression of SOS2, and collecting the SOS2 protein.

[0025] In another preferred embodiment, the present invention provides a method of making a transgenic plant comprising introducing the polynucleotides of the invention into the plant.

[0026] In another preferred embodiment, the present invention provides method of increasing the salt tolerance of a plant in need thereof, comprising introducing the polynucleotides of the invention into said plant.

[0027] In another preferred embodiment, the present invention provides an isolated polypeptide comprising the amino acid sequence in SEQ ID NO:2 or those proteins that are at least 70%, preferably 80%, preferably 90% and preferably 95% identity to SEQ ID NO:2. Preferably, the polypeptides have Na+/K+ transporter activity.

BRIEF DESCRIPTION OF THE FIGURES

[0028] A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

[0029]FIG. 1. Positional cloning of the SOS1 gene. (A) Physical mapping of SOS1. All the SSLP markers shown except ngal 145 were developed in this study based on sequence information of the bacterial artificial chromosomes (BACs). The BAC contig was assembled based on information available at http://www.Arabidopsis.org/cgi-bin/maps incorporated herein by reference. (B) Structure of the SOS1 gene. Positions are relative to the initiation codon. Filled boxes indicate the open reading frame and lines between boxes indicate introns.

[0030]FIG. 2. Complementation of sos1 by 35S-SOS1. Seven-day-old seedlings grown on MS agar medium were transferred to MS medium supplemented with 100 mM NaCl. The picture was taken after 10 days of treatment on-the NaCl medium. Left, wild type plants (WT). Center, sos1-1 mutant plants. Right, transgenic sos1-1 plants containing the wild type SOS1 gene under control of the CaMV 35S promoter. These plants did not show any difference when grown on MS medium without supplementation of NaCl.

[0031]FIG. 3. SOS1 is predicted to encode a transmembrane protein. (A) The deduced amino acid sequence of SOS1. The 12 putative transmembrane domains (TM) are underlined. (B) Hydrophobicity plot of SOS1. The hydrophobicity values were calculated by the program Tmpred available at http://www.ch.embnet.org/software/TMPRED form.html, incorporated herein by reference.

[0032]FIG. 4. SOS1, is similar to Na⁺/H⁺ antiporters. (A) Alignment of SOSI (accession number AF256224) with Na⁺/H⁺ antiporters NHE1 from Chinese hamster (P48761) and NhaP from Pseudomonas aeruginosa (BAA31695). The sequences were aligned by the program ClustalW (http://dot.imgen.bcm.tmc.edu:9331/multi-align/Options/clustalw.html, incorporated herein by reference). Amino acids identical in at least two proteins are highlighted in black and conservative substitutions in grey. * indicates conserved residues that were substituted in sos1 mutant alleles. (B) Phylogenetic analysis of SOS1 and other representative Na⁺/H⁺ antiporters. Multiple sequence alignment was performed with ClustalW. The alignment is based on the N-terminal 450 amino acids of SOS1. Evolutionary distances were calculated by the Neighbor Joining method and the phylogenetic tree was drawn by the program Drawgram (http://bioweb.pasteur.fr/seqanal/phylogeny/phylip-uk.html, incorporated herein by reference). The accession number and source of each of the other representative Na⁺/H⁺ antiporters are as follows: NHE1 (P19634), Homo sapiens; NHE2 (AAD41635), Homo sapiens; NHE3 (P48764), Homo sapiens; NHE4 (P26434), Rattus norvegicus; NIBS (AAC98696.1), Homo sapiens; NHE6 (NP_(—)006350), Homo sapiens; NHA1 (NP_(—)013239), Saccharomyces cerevisiae; NHX1 (NP 010744), Saccharomyces cerevisiae; AtNHX1 (AAD16946.1), Arabidopsis thaliana; SOD2 (CAA77796.1), Schizosaccharomyces pombe; NhaA (P13738), Escherichia coli; NhaP (BAA31695.1), Pseudomonas aeruginosa.

[0033]FIG. 5. Diagrammatic representation of SOS1 structure. The diagram was drawn based on the prediction of hydrophobicity profile of SOS1. Putative transmembrane helices are shown as cylinders. The positions of mutations in sos1 alleles are indicated.

[0034]FIG. 6. SOS1 expression is up-regulated by NaCl stress and is under control of the SOS3/SOS2 regulatory pathway. (A) SOS1 expression is specifically up-regulated by NaCl stress in wild type Arabidopsis seedlings. (B) Up-regulation of SOS1 expression in roots and shoots of wild type plants. (C)SOS1 expression in sos2-1 mutant seedlings. (D) SOS1 expression in sos3-1 mutant seedlings. The same RNA blots were hybridized successively with SOS1, RD29A and actin cDNA probes. Actin was used as loading control and RD29A as control for the stress treatments. C, control treatment.

[0035]FIG. 7. Nucleotide sequence of the SOS1 gene (Genbank accession number AF256224).

[0036]FIG. 8. Overexpression of SOS1 improves salt tolerance of Arabidopsis plants. Transformed plants overexpressing SOS1 and control plants that were transformed with a vector only were compared for their salt tolerance. All plants were grown in soil on a long-day cycle (16 hours light, 8 hours dark). The first 13 days after germination the plants were watered with a diluted nutrient solution (⅛ MS) as needed. Starting on the 14^(th) day, this solution was supplemented with NaCl. The supplementations consisted of four increasingly higher concentrations (50 mM, 100 mM, 150 mM, and 200 mM) of NaCl. The plants were treated for four days at each concentration, for a total of 16 days. On the 16^(th) day the picture shown in the figure was taken.

DETAILED DESCRIPTION OF THE INVENTION

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art of molecular biology. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described herein. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be limiting.

[0038] Reference is made to standard textbooks of molecular biology that contain definitions and methods and means for carrying out basic techniques, encompassed by the present invention. See, for example, Maniatis et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, New York (1982) and Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, New York (1989); Methods in Plant Molecular Biology, Maliga et al, Eds., Cold Spring Harbor Laboratory Press, New York (1995); Arabidopsis, Meyerowitz et al, Eds., Cold Spring Harbor Laboratory Press, New York (1994) and the various references cited therein.

[0039] The term “plant” includes whole plants, plant organs (e.g., leaves, stems, roots, etc.), seeds and plant cells and progeny of same. The class of plants which can be used in the methods of the invention is generally as broad as the class of higher plants amenable to transformation techniques, including both monocotyledonous and dicotyledonous plants. Preferred plants include rice, corn, wheat, cotton, peanut, and soybean.

[0040] Thus, in one embodiment of the present invention, the salt tolerance of a plant can be enhanced or increased by increasing the amount of protein available in the plant, preferably by the enhancement of the SOS1 gene in the plant.

[0041] Thus, one embodiment of the present invention are plant cells carrying the polynucleotides of the present invention, and preferably transgenic plants carrying the isolated polynucleotides of the present invention.

[0042] As used herein, the term “enhancement” means increasing the intracellular activity of one or more enzymes in a plant cell and/or plant which are encoded by the corresponding DNA. Enhancement can be achieved with the aid of various manipulations of the bacterial cell. In order to achieve enhancement, particularly over-expression, the number of copies of the corresponding gene can be increased, a strong promoter can be used, or the promoter- and regulation region or the ribosome binding site which is situated upstream of the structural gene can be mutated. Expression cassettes which are incorporated upstream of the structural gene act in the same manner. In addition, it is possible to increase expression by employing inducible promoters. A gene can also be used which encodes a corresponding enzyme with a high activity. Expression can also be improved by measures for extending the life of the mRNA. Furthermore, enzyme activity as a whole is increased by preventing the degradation of the enzyme. Moreover, these measures can optionally be combined in any desired manner. These and other methods for altering gene activity in a plant are known as described, for example, in Methods in Plant Molecular Biology, Maliga et al, Eds., Cold Spring Harbor Laboratory Press, New York (1995).

[0043] A gene can also be used which encodes a corresponding or variant enzyme with a high activity. Preferably the corresponding enzyme has a greater activity than the native form of the enzyme, more preferably at least in the range of 5, 10, 25% or 50% more activity, most preferably more than twice the activity of the native enzyme.

[0044] In the context of the present Application, a polynucleotide sequence is “homologous” with he sequence according to the invention if at least 70%, preferably at least 80%, most preferably at least 90% of its base composition and base sequence corresponds to the sequence according to the invention. According to the invention, a “homologous protein” is to be understood to comprise proteins which contain an amino acid sequence at least 70% of which, preferably at least 80% of which, most preferably at least 90% of which, corresponds to the amino acid sequence which is encoded by the SOS1 gene (SEQ ID No.1), wherein corresponds is to be understood to mean that the corresponding amino acids are either identical or are mutually homologous amino acids. The expression “homologous amino acids” denotes those which have corresponding properties, particularly with regard to their charge, hydrophobic character, steric properties, etc.

[0045] Homology, sequence similarity or sequence identity of nucleotide or amino acid sequences may be determined conventionally by using known software or computer programs such as the BesiFit or Gap pairwise comparison programs (GCG Wisconsin Package, Genetics Computer Group, 575 Science Drive, Madison, Wis. 53711). BestFit uses the local homology algorithm of Smith and Waterman, Advances in Applied Mathematics 2: 482-489 (1981), to find the best segment of identity or similarity between two sequences. Gap performs global alignments: all of one sequence with all of another similar sequence using the method of Needleman and Wunsch, J. Mol. Biol. 48:443-453 (1970). When using a sequence alignment:program such as BestFit, to determine the degree of sequence homology, similarity or identity, the default setting may be used, or an appropriate scoring matrix may be selected to optimize identity, similarity or homology scores. Similarly, when using a program such as BestFit to determine sequence identity, similarity or homology between two different amino acid sequences, the default settings may be used, or an appropriate scoring matrix, such as blosum45 or blosum80, may be selected to optimize identity, similarity or homology scores.

[0046] The present invention also relates to polynucleotides which contain the complete gene with the polynucleotide sequence corresponding to SEQ ID No. 1 or fragments thereof, and which can be obtained by screening by means of the hybridization of a corresponding gene bank with a probe which contains the sequence of said polynucleotide corresponding to SEQ ID No. 1 or a fragment thereof, and isolation of said DNA sequence.

[0047] Polynucleotide sequences according to the invention are suitable as hybridization probes for RNA, cDNA and DNA, in order to isolate those cDNAs or genes which exhibit a high degree of similarity to the sequence of the SOS1 gene.

[0048] Polynucleotide sequences according to the invention are also suitable as primers for polymerase chain reaction (PCR) for the production of DNA which encodes an enzyme having activity of a Na⁺/H⁺ transporter.

[0049] Oligonucleotides such as these, which serve as probes or primers, can contain more than 30, preferably up to 30, more preferably up to 20, most preferably at least 15 successive nucleotides. Oligonucleotides with a length of at least 40 or 50 nucleotides are also suitable.

[0050] The term “isolated” means separated from its natural environment.

[0051] The term “polynucleotide” refers in general to polyribonucleotides and polydeoxyribonucleotides, and can denote an unmodified RNA or DNA or a modified RNA or DNA.

[0052] The term “polypeptides” is to be understood to mean peptides or proteins which contain two or more amino acids which are bound via peptide bonds.

[0053] The polypeptides according to invention include polypeptides corresponding to SEQ ID No. 2, particularly those with the biological activity of a Na⁺/H⁺ transporter, and also includes those, at least 70% of which, preferably at least 80% of which, are homologous with the polypeptide corresponding to SEQ ID No. 2, and most preferably those which exhibit a homology of least 90% to 95% with the polypeptide corresponding to SEQ ID No. 2 and which have the cited activity.

[0054] The invention also relates to coding DNA sequences which result from SEQ ID No. 1 by degeneration of the genetic code. In the same manner, the invention further relates to DNA sequences which hybridize with SEQ ID No. 1 or with parts of SEQ ID No. 1. Moreover, one skilled in the art is also aware of conservative amino acid replacements such as the replacement of glycine by alanine or of aspartic acid by glutamic acid in proteins as “sense mutations” which do not result in any fundamental change in the activity of the protein, i.e. which are functionally neutral. It is also known that changes at the N- and/or C-terminus of a protein do not substantially impair the function thereof, and may even stabilise said function.

[0055] In the same manner, the present invention also relates to DNA sequences which hybridize with SEQ ID No. 1 or with parts of SEQ ID No. 1. Finally, the present invention relates to DNA sequences which are produced by polymerase chain reaction (PCR) using oligonucleotide primers which result from SEQ ID No.1. Oligonucleotides of this type typically have a length of at least 15 nucleotides.

[0056] The terms “stringent conditions” or “stringent hybridization conditions” includes reference to conditions under which a polynucleotide will hybridize to its target sequence, to a detectably greater degree than other sequences (e.g., at least 2-fold over background). Stringent conditions are sequence-dependent and will be different in different circumstances. By controlling the stringency of the hybridization and/or washing conditions, target sequences can be identified which are 100% complementary to the probe (homologous probing). Alternatively, stringency conditions can be adjusted to allow some mismatching in sequences so that lower degrees of similarity are detected (heterologous probing).

[0057] Typically, stringent conditions will be those in which the salt concentration is less than about 1.5 M Na ion, typically about 0.01 to 1.0 M Na ion concentration (or other salts) at pH 7.0 to 8.3 and the temperature is at least about 30° C. for short probes (e.g., 10 to 50 nucleotides) and at least about 60° C. for long probes (e.g., greater than 50 nucleotides). Stringent conditions may also be achieved with the addition of destabilizing agents such as formamide. Exemplary low stringency conditions include hybridization with a buffer solution of 30 to 35% formamide, 1 M NaCl, 1% SDS (sodium dodecyl sulphate) at 37° C., and a wash in 1× to 2×SSC (20×SSC=3.0 M NaCl/0.3 M trisodium citrate) at 50 to 55° C. Exemplary moderate stringency conditions include hybridization in 40 to 45% formamide, 1 M NaCl, 1% SDS at 37° C., and a wash in 0.5× to 1×SSC at 55 to 60° C. Exemplary high stringency conditions include hybridization in 50% formamide, 1 M NaCl, 1% SDS at 37° C., and a wash in 0.1×SSC at 60 to 65° C.

[0058] Specificity is typically the function of post-hybridization washes, the critical factors being the ionic strength and temperature of the final wash solution. For DNA—DNA hybrids, the Tm can be approximated from the equation of Meinkoth and Wahl, Anal. Biochem., 138:267-284 (1984): Tm=81.5° C.+16.6 (log M)+0.41 (% GC)-0.61 (% form)-500/L; where M is the molarity of monovalent cations, % GC is the percentage of guanosine and cytosine nucleotides in the DNA, % form is the percentage of formamide in the hybridization solution, and L is the length of the hybrid in base pairs. The Tm is the temperature (under defined ionic strength and pH) at which 50% of a complementary target sequence hybridizes to a perfectly matched probe. Tm is reduced by about 1° C. for each 1% of mismatching; thus, Tm, hybridization and/or wash conditions can be adjusted to hybridize to sequences of the desired identity. For example, if sequences with approximately 90% identity are sought, the Tm can be decreased 10° C. Generally, stringent conditions are selected to be about 5° C. lower than the thermal melting point (Tm) for the specific sequence and its complement at a defined ionic strength and pH. However, severely stringent conditions can utilize a hybridization and/or wash at 1, 2, 3, or 4° C. lower than the thermal melting point (Tm); moderately stringent conditions can utilize a hybridization and/or wash at 6, 7, 8, 9, or 10° C. lower than the thermal melting point (Tm); low stringency conditions can utilize a hybridization and/or wash at 11, 12, 13, 14, 15, or 20° C. lower than the thermal melting point (Tm). Using the equation, hybridization and wash compositions, and desired Tm, those of ordinary skill will understand that variations in the stringency of hybridization and/or wash solutions are inherently described. If the desired degree of mismatching results in a Tm of less than 45° C. (aqueous solution) or 32° C. (formamide solution) it is preferred to increase the SSC concentration so that a higher temperature can be used. An extensive guide to the hybridization of nucleic acids is found in Current Protocols in Molecular Biology, Chapter 2, Ausubel, et al., Eds., Greene Publishing and Wiley-Interscience, New York (2000).

[0059] Thus, with the foregoing information, the skilled artisan can identify and isolated polynucleotides which are substantially similar to the present polynucleotides. In so isolating such a polynucleotide, the polynucleotide can be used as the present polynucleotide in, for example, increasing the salt tolerance of a plant.

[0060] One embodiment of the present invention is methods of screening for polynucleotides which have substantial homology to the polynucleotides of the present invention, preferably those polynucleotides encode a protein having Na⁺/H⁺ transporter activity.

[0061] The polynucleotide sequences of the present invention can be carried on one of more suitable plasmid vectors, as known in the art for plants or the like.

[0062] In one embodiment, it may be advantageous for propagating the polynucleotide to carry it in a bacterial or fungal strain with the appropriate vector suitable for the cell type. Common methods of propagating polynucleotides and producing proteins in these cell types are known in the art and are described, for example, in Maniatis et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, New York (1982) and Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, New York (1989).

SPECIFIC EMBODIMENTS OF THE INVENTION

[0063] MATERIALS AND METHODS

[0064] Genetic Mapping

[0065] sos1 mutant plants in the Columbia (Col) background were crossed to wild type plants of the Landsberg (Ler) ecotype. sos mutants were selected from the segregating F2 population by the root-bending assay (11). Genomic DNA from 1663 individual mutant F2 plants was analyzed for cosegragation with SSLP markers. For the fine mapping of SOS1, 7 SSLP markers were-developed based on genomic sequences of the BAC clones at the top of chromosome 2. The primer pairs for the SSLP markers that are polymorphic between Col and Ler are as follows: T20F6-1-F: 5′-GGATGATGATCGATTCGGAT-3′ T20F6-1-R: 5′-ATCTGACTCATAGGATATCG-3′ ngal 145-F: 5′-CCTTCACATCCAAAACCCAC-3′ ngal 145-R: 5′-GCACATACCCACAACCAGAA-3′ F5O4-3-F: 5′-GAATGTTTTGAAGGATATCTCAG-3′ F5O4-3-R: 5′-GAAAAATGGAGCACGAAATAAGC-3′ F14H20-3-F: 5′-CCCGAGATTAATACACAATC-3′ F14H20-3-R: 5′-GCAGATTATGTAATTGTGACC-3′ T23K3-1-F: 5′-TCGTGTTTACCGGGTCGGAT-3′ T23K3-1-R: 5′-TGATGAGAATCTTAGCGAGC-3′ CCC-1-F: 5′-TGGTAAGACCAAATTACACTC-3′ CCC-I-R: 5′-CGTAATTAAAATGTGTTAAACCG-3′ F10A8-1-F: 5′-AACCGCATAGTACAATGCAG-3′ F10A8-1-R: 5′-CGGTAAAGATCAACTAATAACG-3′ F23H14-3-F: 5′-AACGGAAACGGCAACTAGAC-3′ F23H14-3-R: 5′-ACCCTAAATGTTTCGATTCG-3′

[0066] DNA Sequencing

[0067] To determine the nucleotide sequence of SOS1 gene in sos1 mutant alleles, synthetic oligonucleotide primers were made that would enable sequencing of the entire gene. Overlapping fragments encompassing the entire SOSI gene were PCR amplified by using these primers. The amplified products were sequenced on both strands. To avoid errors due to PCR, three independent PCR samples were mixed and batch sequenced.

[0068] Isolation of cDNA

[0069] cDNA containing the complete SOS1 open reading frame was obtained by reverse transcription (RT)-PCR amplification. RNA, from salt-treated Col wild type plants was used as tem plate for the RT-PCR. Three overlapping cDNA fragments obtained from RT-PCR were mixed as the template to amplify a full length cDNA which was then cloned into pCR-Blunt II-TOPO Vector (Invitrogen).

[0070] Plant Transformation and Complementation Test SOS1 cDNA containing the entire open reading frame was cloned into the XbaI and SacI sites of pBI121. The construct was introduced into Agrobacterium GV3101 strain, and the resulting bacteria were used to transform sos1-1 mutant plants by vacuum infiltration (18). Kanamycin resistant T2 transgenic plants were selected and subjected to complementation tests on MS agar medium supplemented with 100 mM NaCl.

[0071] RNA Analysis

[0072] Arabidopsis seedlings were grown on MS agar medium under continuous light (11). Ten-day-old seedlings were used for different treatments. For salt treatment, the seedlings were transferred onto a Whatman filter paper soaked with 3 mM NaCl and treated for 5 h. For ABA treatment, the seedlings were sprayed with 10 μM ABA and kept for 3 h. For cold treatment, the seedlings on MS agar medium were incubated at 0° C. for 24 h. To determine gene expression in root and shoot separately, seedlings were grown on agar surface in vertical plates for 10, days, treated with NaCl by immersing the roots in MS nutrient solution supplemented with 200 mM NaCl for 6 h. RNA extraction and Northern analysis were carried out as described (13).

[0073] RESULTS

[0074] Positional Cloning of SOS1

[0075] By examining several PCR based molecular markers, we found that the SSLP marker ngal 145 near the top of chromosome 2 is closely linked to the sos1 mutation. Seven new SSLP markers were then developed based on the genomic, sequence of BAC clones at the top of chromosome 2. Fine mapping using these markers delimited SOS1 to about 70 kb region between the molecular markers T23K3-1 and F14H₂O-3 (FIG. 1A). Candidate genes in this region were amplified from soil mutants and sequenced. The sequence analysis revealed that a putative gene, F14H20.5, contains a 2 bp deletion in the sos1-13 mutant allele generated by fast neutron bombardment. Further analyses showed that all sos1 alleles contain mutations in this putative gene and each mutation causes a change in the amino acid sequence (Table 1). Furthermore, expression of this candidate gene under control of the CaMV ³⁵S promoter complemented the salt-hypersensitive phenotype of sos1-1 mutant plants (FIG. 2). When sos1-1 mutant seedlings were treated with 100 mM NaCl, their growth was arrested. In these mutant plants, older leaves became chlorotic while young leaves became dark in color. In contrast, sos1-1 mutant plants containing the 35S-SOS1 transgene could grow, and remained green under 100 mM NaCl treatment, as did the wild type plants. Based on these results, we conclude that this putative gene is SOS1.

[0076] SOS1 Encodes a Putative Na⁺/H⁺ Antiporter

[0077] The SOS1 open reading frame was determined by sequencing several overlapping cDNAs obtained from young Arabidopsis seedlings by reverse transcriptase polymerase chain reaction. Comparison with the genomic sequence revealed that SOS1 has 22 introns and 23 exons (FIG. 1B). SOS1 is predicted to encode a polypeptide of 1146 amino acid residues (FIG. 3A) with a theoretical molecular mass of 127 kDa. Hydrophobicity plot analysis showed that the N-terminal portion of SOS1 is highly hydrophobic and has 12 predicted transmembrane domains (FIG. 3B). Database searches revealed substantial similarities between the transmembrane region of SOS1 and Na⁺/H⁺ antiporters of animal or microbial origins (FIG. 4A). Over a stretch of 342 amino acid residues (113-443), SOS1 has 26% identity and 45% similiarity with NHE1 from Chinese hamster (19). The highest sequence similarities for SOS1 are with the “eucaryotic” type Na⁺/H⁺ antiporters from bacteria, of which only NhaP from Pseudomonas aeruginosa has been functionally characterized (20). SOS1 exhibits 31% identity and 48% similarity with the NhaP sequence over a stretch of 289 amino acids (131-408 in SOS1). The C-terminal portion of SOS1 is hydrophilic and predicted to reside in the cytoplasm (FIG. 5). The long hydrophilic carboxyl-terminal tail makes SOS1 the largest Na⁺/H⁺ antiporter sequence known to date. No similarities were Found between the SOS1 tail region and other amino acid sequences in the GenBank database.

[0078] Phylogenetic analysis showed that SOS1 clusters with plasma membrane Na⁺/H⁺ antiporters such as SOD2, NHa1, NhaA. and NhaP (FIG. 4B). SOD2 and NHA1 function on the plasma membrane of S. pombe and S. cerevisiae, respectively, to export Na⁺ from cytosol to the extracellular space (21, 22, 23). NhaA and NhaP are Na⁺/H⁺ antiporters that function in Na⁺ efflux in E. coli and P. aeriuginosa, respectively (20, 24). SOS1 is more distantly related to a cluster of orgaruellar Na⁺/H⁺ antiporters such as AtNHX1,. NHX1 or NHE6 (FIG. 4B). AtNHX1 functions on the tonoplast to compartmentalize Na⁺ into the vacuole of Arabidopsis cells (6, 7). NHX1 plays a role in transporting Na⁺ to the yeast prevacuolar compartment (25, 26). The animal Na⁺/H⁺ antiporter NHE6 has been reported to have a mitochondrial localization (2′7). SOS1 does not cluster with plasma membrane Na⁺/H⁺ antiporters from animals, which function in mediating Na⁺ influx (28). These results suggest that SOS1 is distinct from vacuolar Na⁺/H⁺ antiporters, and may function at plant cell plasma membrane to mediate Na⁺ efflux.

[0079] Analysis of sos1 Mutant Alleles Reveals Several Residues and Regions Essential for SOS1 Function

[0080] The SOS1 gene was amplified from thirty-two independent sos1 mutant lines (13) and sequenced to determine the molecular basis of each mutation. Several mutant lines were found to harbor identical mutations (Table 1). Five of the fast neutron alleles result in relatively large deletions and were not assigned specific allele designations because the boundaries of the deletions are not known. Analysis of the various sos1 mutations reveals several amino acid residues and regions essential for SOS1 function. The sos1-3 and sos1-12 alleles contain single amino acid substitutions in the membrane spanning region (FIG. 5). Both mutations affect residues that are conserved in all antiporters (FIG. 4A) and presumably abolish SOS1 antiport activity. Two other single amino acid substitution mutations (i.e. sos1-8 and sos1-9) one found in the hydrophilic tail region (FIG. 5). The sos1-10 allele was obtained from T-DNA mutagenesis and contains a 7-bp deletion that causes a frameshift that truncates the last 40 amino acids from the C-terminus of SOS1 (FIG. 5). Similarly, sos1-2 and sos1-6 mutations also truncate the cytoplasmic tail of SOSI (FIG. 5). These and other mutations that do not affect the transmembrane region reveal an essential role of the tail region for SOS1 function. Like the hydrophilic tail of animal NHE1 antioporters (29), the tail of SOS1 may interact with various regulators of antiport activity. As such, these mutations likely disrupt interaction between SOS1 and its regulators.

[0081] SOS1 Expression Is Up-regulated Specifically by Salt Stress

[0082] To examine the expression of SOS1 gene under stresses, RNA gel blot analysis was performed, SOS1 mRNA was detected without stress treatment but was significantly up-regulated by salt stress (FIG. 6A). Consistent with its specific role in Na⁺ tolerance, SOSI gene expression was not up-regulated by cold stress or ABA (FIG. 6A). In comparison, the RD29A gene was induced by ABA, cold as well as salt stresses. SOS1 mRNA was more abundant in roots than in shoots. In both roots and shoots, SOS1 expression was up-regulated by NaCl stress (FIG. 6B).

[0083] SOS1 Up-Regulation Is Controlled by the SOS3/SOS2 Pathway

[0084] To determine whether NaCl up-regulation of SOS1 is under control of the SOS3/SOS2 regulatory pathway, SOS1 expression in sos2-1 and sos3-1 mutant plants was analyzed. In the sos2 mutant. SOS1 was up-regulated by NaCl stress in the root but not in the shoot (FIG. 6C). In sos3 plants, no SOSI up-regulation was seen in either the root or shoot (FIG. 6D). These results show that SOS1 expression is regulated at least in part by the SOS3/SOS2 pathway.

[0085] DISCUSSION

[0086] SOS1 is a genetic locus that was previously identified as essential for plant salt tolerance (11). Mutations in SOS1 render Arabidopsis plants extremely sensitive to high Na⁺ or low K⁺ environment (11, 13). In order to understand how the SOS1 gene functions in salt tolerance, it was necessary to clone this gene. Even though several sos1 mutant lines were recovered from a T-DNA insertion population, the T-DNA did not co-segregate with the sos1 mutant phenotype (13). Therefore, a map-based strategy had to be utilized to clone the SOS1 gene. Fine genetic mapping narrowed the search of SOS1 to a very short region of chromosome 2. The fine mapping of SOS1 was made possible by the several molecular markers we have developed and the large number of recombinant chromosomes examined. Several candidate genes in the region where SOS1 is mapped were sequenced to identify the sos1 mutation. One of the candidate genes was found to contain a mutation in every sos1 mutant allele. Further confirmation that this candidate is indeed SOS1, came from genetic complementation test.

[0087] The SOS1 protein is predicted to have 12 transmembrane domains in its N-terminal part. Throughout this transmembrane region, SOS1 shows substantial sequence similarities with Na⁺/H+antiporters from microbes and animals. The sequence similarities combined with the Na⁺ hypersensitive phenotype of sos1 mutant plants strongly indicate that SOS1 is a Na⁺/H⁺ antiporter. Phylogenetic analysis showed that SOSI is more closely related to plasma membrane Na⁺/H⁺ antiporters from microorganisms than to the vacuolar antiporters from either plants or fungi. This suggests that SOS1 is a plasma membrane Na⁺/H⁺ antiporter in Arabidopsis, As such, SOS1 is expected to function in exporting Na⁺ from the cytosol to the extracellular space, to prevent rapid accumulation of Na⁺ in the cytoplasm.

[0088] SOS1 is predicted to have a cytoplasmic tail of approximately 700 amino acids in length. Sequence analysis of the multitude of sos1 mutant alleles revealed that both the tail and transmembrane regions of SOS1 are necessary for its function in plant salt tolerance. The sos1-3, sos1-8, sos1-9 and sos1-12 mutations each causes a single amino acid substitution in the SOS1 protein. Two of these substitutions occur in the transmembrane region and the other two in the tail. These four residues are clearly critical for SOS1 function. The data presented herein on the sos1 mutant lesions provide a wealth of information that will be valuable for detailed structure-function analysis.

[0089] SOS1 gene expression is up-regulated by NaCl stress. This is consistent with its role in Na⁺ tolerance. It has been known that NaCl stress also up-regulates the expression of genes encoding plasma membrane H⁺-ATPases (30). Increased H⁺-ATPase expression would provide a greater proton motive force that is necessary for elevated Na⁺/H⁺ antiporter activity.

[0090] The SOS3 calcium sensor physically interacts with the SOS2 protein kinase (17). In the presence of calcium, SOS3 activates SOS2 kinase activity. The SOS3-SOS2 kinase complex represents a regulatory pathway that specifically controls Na⁺ and K⁺ homeostasis and plant salt tolerance. Results presented in this paper suggest that one output of this pathway is the up-regulation of SOS1 expression under NaCl stress. The sos3 mutation abolishes SOS1 up-regulation in both the root and shoot. In the sos2 mutant, SOS1 up-regulation in the shoot but not in root was disrupted. The fact that SOS1 expression is still up-regulated in the root of sos1 mutant indicates that there may be a functionally redundant root-specific SOS2-like kinase(s). The regulation of SOS1 gene expression by the SOS2/SOS3 pathway is consistent with previous genetic evidence suggesting that SOS1 functions in the same pathway as SOS2 and SOS3 (12, 13).

[0091] SOS1 is essential for the homeostasis of both Na+ and K⁺. Under NaCl stress, sos1 mutant plants accumulate less Na⁺ as well as less W (11, 31). SOS1 gene expression is concentrated in cells surrounding the xylem, suggesting that SOS1 may function in loading Na⁺ into the xylem for long distance transport (our unpublished data). A xylem loading function of SOS1 would be consistent with sos1 mutant plants accumulating less Na⁺. Preferential expression of SOS1 at the symplast/xylem boundary would also help explain the K⁺ transport defect of sos1 mutant plants. It is well known that H⁺ and Na⁺ transport is closely linked at the xylem/symplast interface (32). The effect of SOS1 on K⁺ transport might be through its effect on W gradient across the cell membrane of stellar cells. For example, a K⁺-H⁺ symporter activity could be coupled with SOS1 via H⁺ cycling and such a symporter may be required for high affinity W transport into the xylem. It is also possible that a K⁺/Na⁺ symporter is coupled with SOS1 via Na⁺ cycling. TABLE 1 Molecular basis of sos1 mutations. Mutant line Allele Mutagen Nucleotide change Protein change ssr1, Icss-3, Icss1-18 sos1-1 EMS ▴14 bp, 1330-1343 frameshift ss1-6, ss3-13 sos1-2 EMS C5410-T stop ss1-16, Icss1-24 sos1-3 EMS C2520-T Arg-365-Cys IIcss1-13, IIcss1-22 sos1-4 EMS G-2480-A stop Icss1-10 sos1-5 EMS G2766-A splicing junction Icss1-25 sos1-6 EMS G3652-A stop IIcss1-59, css1-61 sos1-7 EMS ▴1 bp, 4539 frameshift Icss2-21 sos1-8 EMS G-4594-A Gly-777-Glu Icss2-7 sos1-9 EMS G-4615-A Gly-784 = Asp tss2-1, p2901-3503 2-1 sos1-10 T-DNA ▴63 bp, 2792-2854 splicing junction P800 1-2, p800 1-3 sos1-11 T-DNA ▴7 bp, 5953-5959 frameshift FN50css2-3, FN50css3- sos1-12 fast neutron G-668-A Gly-136-Glu 22, FN75cssl-24, FN75css1-14, FN75css3- 18 FN50css2-9, FN75css1- sos1-13 fast neutron ▴2 bp, 5149-5150 frameshift 22, FN75css1-23 FN50css1-8, FN50css3-3, fast neutron Whole gene deletions FN75css1-17, B46, B47

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1 20 1 6076 DNA Arabidopsis thaliana CDS (1)..(226) 1 atg acg act gta atc gac gcg acg atg gcg tat aga ttt ctg gag gaa 48 Met Thr Thr Val Ile Asp Ala Thr Met Ala Tyr Arg Phe Leu Glu Glu 1 5 10 15 gcg acc gat tcg tct tct tct tct tct tct tcc aaa cta gaa tct agc 96 Ala Thr Asp Ser Ser Ser Ser Ser Ser Ser Ser Lys Leu Glu Ser Ser 20 25 30 cct gtc gac gcc gtt ctc ttc gtc gga atg tct ctg gta ctc ggt att 144 Pro Val Asp Ala Val Leu Phe Val Gly Met Ser Leu Val Leu Gly Ile 35 40 45 gct tct agg cac ttg ctt cgt gga act agg gtt cct tac act gtc gct 192 Ala Ser Arg His Leu Leu Arg Gly Thr Arg Val Pro Tyr Thr Val Ala 50 55 60 ctt ctc gtt atc gga att gct ctt gga tct ctc g gttcgatttc 236 Leu Leu Val Ile Gly Ile Ala Leu Gly Ser Leu 65 70 75 gttccatgga atttctgatt tcttcatctg ttttaatcct tgaagtcaac gtaatcatgc 296 ttaattgcta attcatgttg tttggtgttt cag aa tat gga gct aaa cat aac 349 Glu Tyr Gly Ala Lys His Asn 80 ctt gga aag atc ggc cat gga att cgt atc t gtaagttttt agtttcgaat 400 Leu Gly Lys Ile Gly His Gly Ile Arg Ile 85 90 ttttcttctc ttccatggct ggctttgtaa gaactataga atcaatgtta ttgtgcag 458 gg aat gag atc gat cca gaa ctt ctt tta gct gtt ttt ctt ccg gct 505 Trp Asn Glu Ile Asp Pro Glu Leu Leu Leu Ala Val Phe Leu Pro Ala 95 100 105 ctt ctt ttc gag agt tcg ttt tca atg gaa gtt cac caa att aag 550 Leu Leu Phe Glu Ser Ser Phe Ser Met Glu Val His Gln Ile Lys 110 115 120 gtttattcct ctggctctaa ttcctagtta agcttaaagg ttaagagaaa taggtactga 610 atacttgcat gattctttag agg tgt ctg gga caa atg gtg tta ctt gct gtc 663 Arg Cys Leu Gly Gln Met Val Leu Leu Ala Val 125 130 cct gga gtt ctt att tca aca gct tgt ctt gga tcg ctt gtg aag 708 Pro Gly Val Leu Ile Ser Thr Ala Cys Leu Gly Ser Leu Val Lys 135 140 145 gtatgaatta gcctggttgg tattaagtag ctgtcctgaa aacaaagaaa gacaaatcga 768 ttattatgtt atgaaactat acttgctata tgcag gtc acg ttt ccg tat gaa 821 Val Thr Phe Pro Tyr Glu 150 155 tgg gac tgg aaa acg tcc ttg ttg ctt ggg gga ctt tta agt gct act 869 Trp Asp Trp Lys Thr Ser Leu Leu Leu Gly Gly Leu Leu Ser Ala Thr 160 165 170 gat ccg gtt gct gtt gtt gct ttg cta aag gag ctt ggt gct agt aag 917 Asp Pro Val Ala Val Val Ala Leu Leu Lys Glu Leu Gly Ala Ser Lys 175 180 185 aag cta agc acc ata att gaa ggg gaa tcc ctg atg aat gat gg 961 Lys Leu Ser Thr Ile Ile Glu Gly Glu Ser Leu Met Asn Asp Gly 190 195 200 gtaaatgacg ttatcttctg tcatggtttg gttagttttg acatttatgc tcactcttca 1021 tgatttttaa caacaattcc ag g acg gcg att gtt gtt ttc cag tta ttc 1071 Thr Ala Ile Val Val Phe Gln Leu Phe 205 210 tta aag atg gct atg ggg caa aac tct gac tgg agt tct ata atc aaa 1119 Leu Lys Met Ala Met Gly Gln Asn Ser Asp Trp Ser Ser Ile Ile Lys 215 220 225 ttt ctg ctt aaa gtc gca ctt gga gc gtatgtcttg atcttttttc 1165 Phe Leu Leu Lys Val Ala Leu Gly Ala 230 235 atctgttgtt agtgatatca agttgctgct gtgttcttat cagtccaacg tgttcttctg 1225 tctatttag t gta ggc att ggt ctg gcg ttt ggc att gca tca gtt att 1274 Val Gly Ile Gly Leu Ala Phe Gly Ile Ala Ser Val Ile 240 245 tgg ctc aag ttc ata ttc aat gac act gta ata gag att act ctt aca 1322 Trp Leu Lys Phe Ile Phe Asn Asp Thr Val Ile Glu Ile Thr Leu Thr 250 255 260 265 att gca gtg agc tat ttc gca tac tac act gtacgtcttt ctgtagacct 1372 Ile Ala Val Ser Tyr Phe Ala Tyr Tyr Thr 270 275 tgaattcctg tgctaagata ttctctttgt agtaaaactg agagtttatt gtgtgacag 1431 gct caa gag tgg gct ggg gct tct ggt gtt ttg acg gtc atg act ttg 1479 Ala Gln Glu Trp Ala Gly Ala Ser Gly Val Leu Thr Val Met Thr Leu 280 285 290 ggc at gtaaatttca gtgatctcgt tatttttttt ttccctttct tttgttatca 1534 Gly Met tttaagaagt ctcttctcat aaaataactg taacag g ttt tat gct gca ttt gca 1589 Phe Tyr Ala Ala Phe Ala 295 agg aca gcc ttt aaa ggt gac agt caa aaa agc ttg cat cac ttc tg 1636 Arg Thr Ala Phe Lys Gly Asp Ser Gln Lys Ser Leu His His Phe Trp 300 305 310 gtatttccag aacttgtgga atttggactt gtttttttat attgtaactc tatgtaaaag 1696 gttgatctgt gtgatataaa ttttcccggt aacttgtgca g g gaa atg gtt gca 1750 Glu Met Val Ala tat att gca aac act ttg ata ttt atc ctc ag gtaagggtaa attttataga 1802 Tyr Ile Ala Asn Thr Leu Ile Phe Ile Leu Ser 320 325 ctcatatcat gcttgtgctt gccaacccta aaatagaagc tcatgggtag aaaaaagagc 1862 tattttactg cagtctactc tttagcctgg tgttgcaata ttgactgtgt ttctcgtttt 1922 atgtttgcag t ggt gtt gtc att gct gaa ggc att ctc gac agt gat aag 1972 Gly Val Val Ile Ala Glu Gly Ile Leu Asp Ser Asp Lys 335 340 att gcc tac caa g gtgccattat ttaatgttga tagtgtacag tatttttttc 2025 Ile Ala Tyr Gln 345 ctagctaaag taaattttgt gaacatagtt ttgtctgcat tttcgacagt tcactgttaa 2085 ttgaagatga gatctaagtc attacatagg actcccacct gttatcatag ttttctgtcg 2145 ttgttaacac accttactgt tcatggtctt tggttctcga aggatcacta attccataac 2205 gtgaatcagt tacaagaata agaaaaaaac tggcattatt ggttacgaaa tattgagcga 2265 aagttaccac tgtgctagga ctgagacaat tgtattcttt caccagtctg ttattattat 2325 taagtacctg ttagagatgt actgtcttgg aaccatatat tttttctctg gaaccatatc 2385 tgcataaggc acatgatata cttaacttta actatttttt atattttgga tctaacaact 2445 cttcacgacc caaatttctt acag gg aat tca tgg cga ttt ctt ttt ctg 2495 Gly Asn Ser Trp Arg Phe Leu Phe Leu 350 355 cta tac gtt tac atc caa cta tcg cgt gtt gtt gtt gtt gga gtt cta 2543 Leu Tyr Val Tyr Ile Gln Leu Ser Arg Val Val Val Val Gly Val Leu 360 365 370 tat cca ctt tta tgt cgt ttt ggc tat ggt ttg gat tgg aaa gaa tcc 2591 Tyr Pro Leu Leu Cys Arg Phe Gly Tyr Gly Leu Asp Trp Lys Glu Ser 375 380 385 att ata ctc gta tgg tct ggt ttg agg ggc gca gtg gct ctt gca ctt 2639 Ile Ile Leu Val Trp Ser Gly Leu Arg Gly Ala Val Ala Leu Ala Leu 390 395 400 tct tta tcc gtg aag gttaatttta agaacatctg ttaaagttgt tcttctctct 2694 Ser Leu Ser Val Lys 405 taaatttctg cacaatgttt ttttccagcc acattgattc tgtgctgact tactcgcact 2754 catttgattc ag caa tca agc gga aat tca cat atc agc aag gag act gga 2805 Gln Ser Ser Gly Asn Ser His Ile Ser Lys Glu Thr Gly 410 415 420 aca ttg gtaagttagt ctaaagatgt tattgacaac ttaaaatgat tatgcaaatt 2861 Thr Leu attgttttgt ctcttcatat tctcagttct tttgcag ttt ctt ttc ttc acg ggt 2916 Phe Leu Phe Phe Thr Gly 425 430 gga att gtg ttc cta act ctg ata gtt aat gga tcc act acc caa ttt 2964 Gly Ile Val Phe Leu Thr Leu Ile Val Asn Gly Ser Thr Thr Gln Phe 435 440 445 gtt cta cgc ctt ctt cgc atg gat att tta cca gcc ccc aag 3006 Val Leu Arg Leu Leu Arg Met Asp Ile Leu Pro Ala Pro Lys 450 455 460 gtcaaaaact tctctcatac gaataacttt ccgagtttta agtaatcaaa tatatgtgta 3066 aacagagatt tttttgctta tgctttgtat tcatgtgtaa gtgaccgtgt tagcctgagt 3126 ctgagccttt aagctgtata gttcaatagg gtctgtatgt tctagtcagt aatgtattcg 3186 aagaacctta ttagaaacca ctttcctttt gacag aaa cga ata ttg gaa tat 3239 Lys Arg Ile Leu Glu Tyr 465 aca aag tac gaa atg ttg aat aag gcc tta cga gcg ttt caa gat cta 3287 Thr Lys Tyr Glu Met Leu Asn Lys Ala Leu Arg Ala Phe Gln Asp Leu 470 475 480 gga gac gat gag gag cta gga cct gct gac tgg cct aca gtt gaa agt 3335 Gly Asp Asp Glu Glu Leu Gly Pro Ala Asp Trp Pro Thr Val Glu Ser 485 490 495 tat att tca agc cta aaa ggt tca gaa ggg gaa cta gtt cat cat cct 3383 Tyr Ile Ser Ser Leu Lys Gly Ser Glu Gly Glu Leu Val His His Pro 500 505 510 cac aat ggc tct aaa att gga agt ctt gac cct aaa agt tta aag gac 3431 His Asn Gly Ser Lys Ile Gly Ser Leu Asp Pro Lys Ser Leu Lys Asp 515 520 525 530 ata cgt atg cgg ttc tta aat g gtagttatga tcatgtaccc tccaatatac 3483 Ile Arg Met Arg Phe Leu Asn 535 tattttacct ggtagattat tgacactttg aaaattggtt gtgtcag gt gtg caa 3538 Gly Val Gln 540 gca act tac tgg gag atg ctt gat gag ggc aga ata tct gaa gtt act 3586 Ala Thr Tyr Trp Glu Met Leu Asp Glu Gly Arg Ile Ser Glu Val Thr 545 550 555 gct aat att ttg atg cag tca gtg gat gag gcg ctt gat cag gtt tct 3634 Ala Asn Ile Leu Met Gln Ser Val Asp Glu Ala Leu Asp Gln Val Ser 560 565 570 aca act tta tgt gat tgg aga ggt cta aaa cca cat gtc aat ttc cca 3682 Thr Thr Leu Cys Asp Trp Arg Gly Leu Lys Pro His Val Asn Phe Pro 575 580 585 aat tac tac aac ttt ctt cat tct aaa gtt gtc cca cgc aag ttg gtc 3730 Asn Tyr Tyr Asn Phe Leu His Ser Lys Val Val Pro Arg Lys Leu Val 590 595 600 aca tac ttt gct gtc gaa aga cta gaa tct gct tgc tac att tct gct 3778 Thr Tyr Phe Ala Val Glu Arg Leu Glu Ser Ala Cys Tyr Ile Ser Ala 605 610 615 620 gcg ttt ctt cgc gca cat aca att gca cga cag caa ttg tat gat ttt 3826 Ala Phe Leu Arg Ala His Thr Ile Ala Arg Gln Gln Leu Tyr Asp Phe 625 630 635 cta g gtatgtacaa tccatactct gcagtctgca tcacactttg aaaacaatga 3880 Leu ctaagaataa aacttgtacc gtatcatcat taattgtcag agtttttgtt tgcaagtatc 3940 tcaacttagt aagaacaata cattaaccca accctagttt tgtctcatac ttatctatct 4000 tctctacaca g gg gag agt aat att ggt tcc att gta atc aat gaa agt 4049 Gly Glu Ser Asn Ile Gly Ser Ile Val Ile Asn Glu Ser 640 645 650 gaa aag gaa gga gag gaa gca aaa aag ttc ttg gaa aaa gtc cga tct 4097 Glu Lys Glu Gly Glu Glu Ala Lys Lys Phe Leu Glu Lys Val Arg Ser 655 660 665 tca ttt cct cag gttgagagtc ttgtcatttc tttcgggtga cttatctttc 4149 Ser Phe Pro Gln 670 ttgcggtgag gcacatataa tctttgatta acattggttt cag gtt ctc cgt gtt 4204 Val Leu Arg Val gtg aaa aca aaa caa gta aca tat tca gtg ttg aat cat tta ctc ggt 4252 Val Lys Thr Lys Gln Val Thr Tyr Ser Val Leu Asn His Leu Leu Gly 675 680 685 690 tac att gaa aac ctc gag aag gtt ggc ttg ttg gag gaa aaa gaa atc 4300 Tyr Ile Glu Asn Leu Glu Lys Val Gly Leu Leu Glu Glu Lys Glu Ile 695 700 705 gct cat ctt cat gat gct gtc cag gtaccaaatt aaagaatctc attccttcaa 4354 Ala His Leu His Asp Ala Val Gln 710 ctatagtctt gtctcttttg tcttatgctt ttggtcaaat ctatctctgc ag acc ggc 4412 Thr Gly 715 ttg aaa aag ctt ttg aga aac cct cca ata gtt aaa ctt cca aaa ttg 4460 Leu Lys Lys Leu Leu Arg Asn Pro Pro Ile Val Lys Leu Pro Lys Leu 720 725 730 agc gac atg atc acc tca cat ccg tta tcg gtt gct ctt cct cct gca 4508 Ser Asp Met Ile Thr Ser His Pro Leu Ser Val Ala Leu Pro Pro Ala 735 740 745 ttt tgt gaa cct tta aaa cac tcg aaa aaa gaa cca atg aaa ctg cgt 4556 Phe Cys Glu Pro Leu Lys His Ser Lys Lys Glu Pro Met Lys Leu Arg 750 755 760 ggt gtc acg ctt tat aaa gaa ggt tca aag cca act gga gtc tgg ctt 4604 Gly Val Thr Leu Tyr Lys Glu Gly Ser Lys Pro Thr Gly Val Trp Leu 765 770 775 780 att ttt gat ggc atc gtt aag gtaacccaaa acttatcttt tacttttaac 4655 Ile Phe Asp Gly Ile Val Lys 785 tcgtaagtct gtatgatcta ttaccttcat aactgaatgt tataacaatc ctacag tgg 4714 Trp aaa agt aag atc tta agc aac aat cac tcg ctg cat cca act ttt tct 4762 Lys Ser Lys Ile Leu Ser Asn Asn His Ser Leu His Pro Thr Phe Ser 790 795 800 cac ggt agt aca ttg gga ctc tac gaa gtc ctc act ggg aag cca tat 4810 His Gly Ser Thr Leu Gly Leu Tyr Glu Val Leu Thr Gly Lys Pro Tyr 805 810 815 820 ctg tgc gac ttg att aca gat tct atg gtt ctt tgc ttt ttc att gat 4858 Leu Cys Asp Leu Ile Thr Asp Ser Met Val Leu Cys Phe Phe Ile Asp 825 830 835 agc gag aaa att cta tca cta caa tca gat tct acc atc gat gat ttc 4906 Ser Glu Lys Ile Leu Ser Leu Gln Ser Asp Ser Thr Ile Asp Asp Phe 840 845 850 ctt tgg cag gtacgtctct attagaatcc attttagaga gactcatttc 4955 Leu Trp Gln 855 ttgattgtta agttgcttca acttttttcg gttttttttg tttgcag gaa agt gca 5011 Glu Ser Ala ttg gtt ctt ctc aaa ctc ttg cgt cct cag ata ttt gaa agt gtg gca 5059 Leu Val Leu Leu Lys Leu Leu Arg Pro Gln Ile Phe Glu Ser Val Ala 860 865 870 atg caa gaa tta cga gcc ctt gtt tca act gaa agc tcg aaa ctt aca 5107 Met Gln Glu Leu Arg Ala Leu Val Ser Thr Glu Ser Ser Lys Leu Thr 875 880 885 890 aca tat gtg acg gga gaa tca atc gaa atc gac tgc aac agc att ggt 5155 Thr Tyr Val Thr Gly Glu Ser Ile Glu Ile Asp Cys Asn Ser Ile Gly 895 900 905 tta tta tta gaa gga ttc gta aaa ccg gtt ggt atc aaa gaa gag ctt 5203 Leu Leu Leu Glu Gly Phe Val Lys Pro Val Gly Ile Lys Glu Glu Leu 910 915 920 ata tca tct ccc gcc gca tta tca cct tct aac ggg aat caa agc ttc 5251 Ile Ser Ser Pro Ala Ala Leu Ser Pro Ser Asn Gly Asn Gln Ser Phe 925 930 935 cat aat tca tca gaa gct tca g gtaattaatt gcacagtaca gcaggatcaa 5303 His Asn Ser Ser Glu Ala Ser 940 945 acctttttaa atgtcagcga atgatataaa tcgaattaaa tcaaaaatgt gttttgtttt 5363 tttgaccaca g gt atc atg aga gtc agt ttc tca caa caa gca aca cag 5412 Gly Ile Met Arg Val Ser Phe Ser Gln Gln Ala Thr Gln 950 955 tat att gtt gag acg aga gca aga gca atc atc ttc aac att gga gca 5460 Tyr Ile Val Glu Thr Arg Ala Arg Ala Ile Ile Phe Asn Ile Gly Ala 960 965 970 ttt gga gct gat agg act cta cat cga aga cca tct tcg tta aca cca 5508 Phe Gly Ala Asp Arg Thr Leu His Arg Arg Pro Ser Ser Leu Thr Pro 975 980 985 990 cca cgt agc tca agc tct gat cag ctt cag aga tca ttt cgt aaa gaa 5556 Pro Arg Ser Ser Ser Ser Asp Gln Leu Gln Arg Ser Phe Arg Lys Glu 995 1000 1005 cac aga ggt ctc atg agc tgg cct gaa aat att tac gcc aaa caa 5601 His Arg Gly Leu Met Ser Trp Pro Glu Asn Ile Tyr Ala Lys Gln 1010 1015 1020 caa caa gag atc aat aaa acg aca tta agt tta tct gaa cga gca 5646 Gln Gln Glu Ile Asn Lys Thr Thr Leu Ser Leu Ser Glu Arg Ala 1025 1030 1035 atg caa ctc agc att ttc ggc agc atg gtaaaaaaga tctcaatgtt 5693 Met Gln Leu Ser Ile Phe Gly Ser Met 1040 1045 gattctttta aaggttgtta tcgatgaact tctcgactaa cctgaaggtt tttatcttct 5753 gatattctcg aatatag gtt aat gtg tac aga agg agt gta agt ttc ggt 5803 Val Asn Val Tyr Arg Arg Ser Val Ser Phe Gly 1050 1055 ggg atc tat aat aac aag tta caa gat aac ttg ttg tac aaa aaa 5848 Gly Ile Tyr Asn Asn Lys Leu Gln Asp Asn Leu Leu Tyr Lys Lys 1060 1065 1070 ctt cca cta aac cca gct caa ggt ctc gtt tca gcc aaa tca gaa 5893 Leu Pro Leu Asn Pro Ala Gln Gly Leu Val Ser Ala Lys Ser Glu 1075 1080 1085 agt tca att gtg acc aag aag cag ctt gaa acc cgt aaa cat gcg 5938 Ser Ser Ile Val Thr Lys Lys Gln Leu Glu Thr Arg Lys His Ala 1090 1095 1100 tgt cag ctt cct ctg aaa ggg gaa agc agc aca agg caa aat acg 5983 Cys Gln Leu Pro Leu Lys Gly Glu Ser Ser Thr Arg Gln Asn Thr 1105 1110 1115 atg gtt gaa tca agc gat gaa gaa gat gaa gat gaa gga atc gtt 6028 Met Val Glu Ser Ser Asp Glu Glu Asp Glu Asp Glu Gly Ile Val 1120 1125 1130 gtg aga atc gat tct ccg agt aaa atc gtt ttc agg aac gat cta 6073 Val Arg Ile Asp Ser Pro Ser Lys Ile Val Phe Arg Asn Asp Leu 1135 1140 1145 tga 6076 2 1146 PRT Arabidopsis thaliana 2 Met Thr Thr Val Ile Asp Ala Thr Met Ala Tyr Arg Phe Leu Glu Glu 1 5 10 15 Ala Thr Asp Ser Ser Ser Ser Ser Ser Ser Ser Lys Leu Glu Ser Ser 20 25 30 Pro Val Asp Ala Val Leu Phe Val Gly Met Ser Leu Val Leu Gly Ile 35 40 45 Ala Ser Arg His Leu Leu Arg Gly Thr Arg Val Pro Tyr Thr Val Ala 50 55 60 Leu Leu Val Ile Gly Ile Ala Leu Gly Ser Leu Glu Tyr Gly Ala Lys 65 70 75 80 His Asn Leu Gly Lys Ile Gly His Gly Ile Arg Ile Trp Asn Glu Ile 85 90 95 Asp Pro Glu Leu Leu Leu Ala Val Phe Leu Pro Ala Leu Leu Phe Glu 100 105 110 Ser Ser Phe Ser Met Glu Val His Gln Ile Lys Arg Cys Leu Gly Gln 115 120 125 Met Val Leu Leu Ala Val Pro Gly Val Leu Ile Ser Thr Ala Cys Leu 130 135 140 Gly Ser Leu Val Lys Val Thr Phe Pro Tyr Glu Trp Asp Trp Lys Thr 145 150 155 160 Ser Leu Leu Leu Gly Gly Leu Leu Ser Ala Thr Asp Pro Val Ala Val 165 170 175 Val Ala Leu Leu Lys Glu Leu Gly Ala Ser Lys Lys Leu Ser Thr Ile 180 185 190 Ile Glu Gly Glu Ser Leu Met Asn Asp Gly Thr Ala Ile Val Val Phe 195 200 205 Gln Leu Phe Leu Lys Met Ala Met Gly Gln Asn Ser Asp Trp Ser Ser 210 215 220 Ile Ile Lys Phe Leu Leu Lys Val Ala Leu Gly Ala Val Gly Ile Gly 225 230 235 240 Leu Ala Phe Gly Ile Ala Ser Val Ile Trp Leu Lys Phe Ile Phe Asn 245 250 255 Asp Thr Val Ile Glu Ile Thr Leu Thr Ile Ala Val Ser Tyr Phe Ala 260 265 270 Tyr Tyr Thr Ala Gln Glu Trp Ala Gly Ala Ser Gly Val Leu Thr Val 275 280 285 Met Thr Leu Gly Met Phe Tyr Ala Ala Phe Ala Arg Thr Ala Phe Lys 290 295 300 Gly Asp Ser Gln Lys Ser Leu His His Phe Trp Glu Met Val Ala Tyr 305 310 315 320 Ile Ala Asn Thr Leu Ile Phe Ile Leu Ser Gly Val Val Ile Ala Glu 325 330 335 Gly Ile Leu Asp Ser Asp Lys Ile Ala Tyr Gln Gly Asn Ser Trp Arg 340 345 350 Phe Leu Phe Leu Leu Tyr Val Tyr Ile Gln Leu Ser Arg Val Val Val 355 360 365 Val Gly Val Leu Tyr Pro Leu Leu Cys Arg Phe Gly Tyr Gly Leu Asp 370 375 380 Trp Lys Glu Ser Ile Ile Leu Val Trp Ser Gly Leu Arg Gly Ala Val 385 390 395 400 Ala Leu Ala Leu Ser Leu Ser Val Lys Gln Ser Ser Gly Asn Ser His 405 410 415 Ile Ser Lys Glu Thr Gly Thr Leu Phe Leu Phe Phe Thr Gly Gly Ile 420 425 430 Val Phe Leu Thr Leu Ile Val Asn Gly Ser Thr Thr Gln Phe Val Leu 435 440 445 Arg Leu Leu Arg Met Asp Ile Leu Pro Ala Pro Lys Lys Arg Ile Leu 450 455 460 Glu Tyr Thr Lys Tyr Glu Met Leu Asn Lys Ala Leu Arg Ala Phe Gln 465 470 475 480 Asp Leu Gly Asp Asp Glu Glu Leu Gly Pro Ala Asp Trp Pro Thr Val 485 490 495 Glu Ser Tyr Ile Ser Ser Leu Lys Gly Ser Glu Gly Glu Leu Val His 500 505 510 His Pro His Asn Gly Ser Lys Ile Gly Ser Leu Asp Pro Lys Ser Leu 515 520 525 Lys Asp Ile Arg Met Arg Phe Leu Asn Gly Val Gln Ala Thr Tyr Trp 530 535 540 Glu Met Leu Asp Glu Gly Arg Ile Ser Glu Val Thr Ala Asn Ile Leu 545 550 555 560 Met Gln Ser Val Asp Glu Ala Leu Asp Gln Val Ser Thr Thr Leu Cys 565 570 575 Asp Trp Arg Gly Leu Lys Pro His Val Asn Phe Pro Asn Tyr Tyr Asn 580 585 590 Phe Leu His Ser Lys Val Val Pro Arg Lys Leu Val Thr Tyr Phe Ala 595 600 605 Val Glu Arg Leu Glu Ser Ala Cys Tyr Ile Ser Ala Ala Phe Leu Arg 610 615 620 Ala His Thr Ile Ala Arg Gln Gln Leu Tyr Asp Phe Leu Gly Glu Ser 625 630 635 640 Asn Ile Gly Ser Ile Val Ile Asn Glu Ser Glu Lys Glu Gly Glu Glu 645 650 655 Ala Lys Lys Phe Leu Glu Lys Val Arg Ser Ser Phe Pro Gln Val Leu 660 665 670 Arg Val Val Lys Thr Lys Gln Val Thr Tyr Ser Val Leu Asn His Leu 675 680 685 Leu Gly Tyr Ile Glu Asn Leu Glu Lys Val Gly Leu Leu Glu Glu Lys 690 695 700 Glu Ile Ala His Leu His Asp Ala Val Gln Thr Gly Leu Lys Lys Leu 705 710 715 720 Leu Arg Asn Pro Pro Ile Val Lys Leu Pro Lys Leu Ser Asp Met Ile 725 730 735 Thr Ser His Pro Leu Ser Val Ala Leu Pro Pro Ala Phe Cys Glu Pro 740 745 750 Leu Lys His Ser Lys Lys Glu Pro Met Lys Leu Arg Gly Val Thr Leu 755 760 765 Tyr Lys Glu Gly Ser Lys Pro Thr Gly Val Trp Leu Ile Phe Asp Gly 770 775 780 Ile Val Lys Trp Lys Ser Lys Ile Leu Ser Asn Asn His Ser Leu His 785 790 795 800 Pro Thr Phe Ser His Gly Ser Thr Leu Gly Leu Tyr Glu Val Leu Thr 805 810 815 Gly Lys Pro Tyr Leu Cys Asp Leu Ile Thr Asp Ser Met Val Leu Cys 820 825 830 Phe Phe Ile Asp Ser Glu Lys Ile Leu Ser Leu Gln Ser Asp Ser Thr 835 840 845 Ile Asp Asp Phe Leu Trp Gln Glu Ser Ala Leu Val Leu Leu Lys Leu 850 855 860 Leu Arg Pro Gln Ile Phe Glu Ser Val Ala Met Gln Glu Leu Arg Ala 865 870 875 880 Leu Val Ser Thr Glu Ser Ser Lys Leu Thr Thr Tyr Val Thr Gly Glu 885 890 895 Ser Ile Glu Ile Asp Cys Asn Ser Ile Gly Leu Leu Leu Glu Gly Phe 900 905 910 Val Lys Pro Val Gly Ile Lys Glu Glu Leu Ile Ser Ser Pro Ala Ala 915 920 925 Leu Ser Pro Ser Asn Gly Asn Gln Ser Phe His Asn Ser Ser Glu Ala 930 935 940 Ser Gly Ile Met Arg Val Ser Phe Ser Gln Gln Ala Thr Gln Tyr Ile 945 950 955 960 Val Glu Thr Arg Ala Arg Ala Ile Ile Phe Asn Ile Gly Ala Phe Gly 965 970 975 Ala Asp Arg Thr Leu His Arg Arg Pro Ser Ser Leu Thr Pro Pro Arg 980 985 990 Ser Ser Ser Ser Asp Gln Leu Gln Arg Ser Phe Arg Lys Glu His Arg 995 1000 1005 Gly Leu Met Ser Trp Pro Glu Asn Ile Tyr Ala Lys Gln Gln Gln 1010 1015 1020 Glu Ile Asn Lys Thr Thr Leu Ser Leu Ser Glu Arg Ala Met Gln 1025 1030 1035 Leu Ser Ile Phe Gly Ser Met Val Asn Val Tyr Arg Arg Ser Val 1040 1045 1050 Ser Phe Gly Gly Ile Tyr Asn Asn Lys Leu Gln Asp Asn Leu Leu 1055 1060 1065 Tyr Lys Lys Leu Pro Leu Asn Pro Ala Gln Gly Leu Val Ser Ala 1070 1075 1080 Lys Ser Glu Ser Ser Ile Val Thr Lys Lys Gln Leu Glu Thr Arg 1085 1090 1095 Lys His Ala Cys Gln Leu Pro Leu Lys Gly Glu Ser Ser Thr Arg 1100 1105 1110 Gln Asn Thr Met Val Glu Ser Ser Asp Glu Glu Asp Glu Asp Glu 1115 1120 1125 Gly Ile Val Val Arg Ile Asp Ser Pro Ser Lys Ile Val Phe Arg 1130 1135 1140 Asn Asp Leu 1145 3 822 PRT Cricetulus griseus 3 Met Met Leu Arg Trp Ser Gly Ile Trp Gly Leu Ser Pro Pro Arg Ile 1 5 10 15 Phe Pro Ser Leu Leu Val Val Val Ala Leu Val Gly Leu Leu Pro Val 20 25 30 Leu Arg Ser His Gly Leu Gln Pro Ser Pro Thr Ala Asn Thr Ile Arg 35 40 45 Gly Ala Glu Pro Pro Arg Glu Arg Ser Ile Gly Asp Val Thr Thr Ala 50 55 60 Pro Ser Glu Pro Val His His Pro Asp Asp Arg Asn Leu Thr Asn Leu 65 70 75 80 His Ile Glu His Gly Ala Lys Thr Leu Arg Lys Ala Phe Pro Val Leu 85 90 95 Asp Ile Asp Tyr Leu His Val Arg Thr Pro Phe Glu Ile Ser Leu Trp 100 105 110 Ile Leu Leu Ala Cys Leu Met Lys Ile Gly Phe His Val Ile Pro Thr 115 120 125 Ile Ser Ser Ile Val Pro Glu Ser Cys Leu Leu Ile Val Val Gly Leu 130 135 140 Leu Val Gly Gly Leu Ile Lys Gly Val Gly Glu Thr Pro Pro Phe Leu 145 150 155 160 Gln Ser Asp Val Phe Phe Leu Phe Leu Leu Pro Pro Ile Ile Leu Asp 165 170 175 Ala Gly Tyr Phe Leu Pro Leu Arg Gln Phe Thr Glu Asn Leu Gly Thr 180 185 190 Ile Leu Ile Phe Ala Val Val Gly Thr Leu Trp Asn Ala Phe Phe Leu 195 200 205 Gly Gly Leu Leu Tyr Ala Val Cys Leu Val Gly Gly Glu Gln Ile Asn 210 215 220 Asn Ile Gly Leu Leu Asp Thr Leu Leu Phe Gly Ser Ile Ile Ser Ala 225 230 235 240 Val Asp Pro Val Ala Val Val Ala Val Phe Glu Glu Ile His Ile Asn 245 250 255 Glu Leu Leu His Ile Leu Val Phe Gly Glu Ser Leu Leu Asn Asp Ala 260 265 270 Val Thr Val Val Leu Tyr His Leu Phe Glu Glu Phe Ala Asn Tyr Asp 275 280 285 Ser Ile Gly Ile Ser Asp Ile Phe Leu Gly Phe Leu Ser Phe Phe Val 290 295 300 Val Ala Leu Gly Gly Val Phe Val Gly Val Val Tyr Gly Val Ile Ala 305 310 315 320 Ala Phe Thr Ser Arg Phe Thr Ser His Ile Arg Val Ile Glu Pro Leu 325 330 335 Phe Val Phe Leu Tyr Ser Tyr Met Ala Tyr Leu Ser Ala Glu Leu Phe 340 345 350 His Leu Ser Gly Ile Met Ala Leu Ile Ala Ser Gly Val Val Met Arg 355 360 365 Pro Tyr Val Glu Ala Asn Ile Ser His Lys Ser His Thr Thr Ile Lys 370 375 380 Tyr Phe Leu Lys Met Trp Ser Ser Val Ser Glu Thr Leu Ile Phe Ile 385 390 395 400 Phe Leu Gly Val Ser Thr Val Ala Gly Ser His Gln Trp Asn Trp Thr 405 410 415 Phe Val Ile Ser Thr Leu Leu Phe Cys Leu Ile Ala Arg Val Leu Gly 420 425 430 Val Leu Val Leu Thr Trp Phe Ile Asn Lys Phe Arg Ile Val Lys Leu 435 440 445 Thr Pro Lys Asp Gln Phe Ile Ile Ala Tyr Gly Gly Leu Arg Gly Ala 450 455 460 Ile Ala Phe Ser Leu Gly Tyr Leu Met Asp Lys Lys His Phe Pro Met 465 470 475 480 Cys Asp Leu Phe Leu Thr Ala Ile Ile Thr Val Ile Phe Phe Thr Val 485 490 495 Phe Val Gln Gly Met Thr Ile Arg Pro Leu Val Asp Leu Leu Ala Val 500 505 510 Lys Lys Lys Gln Glu Thr Lys Arg Ser Ile Asn Glu Glu Ile His Thr 515 520 525 Gln Phe Leu Asp His Leu Leu Thr Gly Ile Glu Asp Ile Cys Gly His 530 535 540 Tyr Gly His His His Trp Lys Asp Lys Leu Asn Arg Phe Asn Lys Lys 545 550 555 560 Tyr Val Lys Lys Cys Leu Ile Ala Gly Glu Arg Ser Lys Glu Pro Gln 565 570 575 Leu Ile Ala Phe Tyr His Lys Met Glu Met Lys Gln Ala Ile Glu Leu 580 585 590 Val Glu Ser Gly Gly Met Gly Lys Ile Pro Ser Ala Val Ser Thr Val 595 600 605 Ser Met Gln Asn Ile His Pro Lys Ser Met Ala Ser Glu Arg Ile Leu 610 615 620 Pro Ala Leu Ser Lys Asp Lys Glu Glu Glu Ile Arg Lys Ile Leu Arg 625 630 635 640 Ser Asn Leu Gln Lys Thr Arg Gln Arg Leu Arg Ser Tyr Asn Arg His 645 650 655 Thr Leu Val Ala Asp Pro Tyr Glu Glu Ala Trp Asn Gln Met Leu Leu 660 665 670 Arg Arg Gln Lys Ala Arg Gln Leu Glu Gln Lys Met Ser Asn Tyr Leu 675 680 685 Thr Val Pro Ala His Lys Leu Asp Ser Pro Thr Met Ser Arg Ala Arg 690 695 700 Ile Gly Ser Asp Pro Leu Ala Tyr Glu Pro Lys Ala Asp Leu Pro Val 705 710 715 720 Ile Thr Ile Asp Pro Ala Ser Pro Gln Ser Pro Glu Ser Val Asp Leu 725 730 735 Val Asn Glu Glu Leu Lys Ala Lys Val Leu Gly Val Asn Arg Asp Pro 740 745 750 Thr Arg Leu Thr Arg Gly Glu Glu Asp Glu Asp Glu Asp Glu Asp Gly 755 760 765 Val Ile Met Met Arg Arg Lys Glu Pro Ser Ser Pro Gly Thr Asp Val 770 775 780 Phe Thr Pro Ala Pro Met Tyr Ser Pro Ser Ser Gln Arg Ile Gln Arg 785 790 795 800 Cys Leu Ser Asp Pro Gly Pro His Pro Glu Pro Gly Glu Gly Glu Pro 805 810 815 Phe Ile Pro Lys Gly Glu 820 4 424 PRT Pseudomonas aeruginosa 4 Met Leu Asp Leu Val Ala Ala Phe Ile Ala Leu Thr Thr Leu Leu Thr 1 5 10 15 Tyr Val Asn Tyr Arg Phe Ile Arg Leu Pro Pro Thr Ile Gly Val Met 20 25 30 Ala Thr Ala Leu Val Phe Ser Leu Ile Val Gln Gly Leu Ser Glu Leu 35 40 45 Gly Tyr Pro Ile Leu Glu Val Glu Met Gln Glu Ile Ile Arg Arg Ile 50 55 60 Asp Phe Ser Glu Val Leu Met Thr Trp Phe Leu Pro Ala Leu Leu Phe 65 70 75 80 Ala Gly Ala Leu His Val Asp Leu Ser Asp Leu Arg Ser Tyr Lys Trp 85 90 95 Pro Ile Gly Leu Leu Ala Thr Ala Gly Val Leu Ile Ala Thr Phe Val 100 105 110 Ile Gly Gly Leu Ala Tyr Tyr Thr Phe Pro Leu Phe Gly Trp Gln Val 115 120 125 Asp Phe Ile Tyr Cys Leu Leu Phe Gly Ala Leu Ile Ser Pro Thr Asp 130 135 140 Pro Ile Ala Val Leu Gly Ile Leu Lys Ser Ala Gly Ala Pro Lys Pro 145 150 155 160 Leu Ala Thr Thr Ile Val Gly Glu Ser Leu Phe Asn Asp Gly Thr Ala 165 170 175 Val Val Val Phe Ala Ile Ile Leu Gly Ile Leu Gln Leu Gly Glu Ala 180 185 190 Pro Thr Val Ser Ala Thr Ala Ile Leu Phe Val Gln Glu Ala Ile Gly 195 200 205 Gly Val Val Phe Gly Ala Val Leu Gly Tyr Gly Val Phe Val Met Met 210 215 220 Arg Gly Ile Asp Gln Tyr Gln Val Glu Val Met Leu Thr Leu Ala Leu 225 230 235 240 Val Ile Gly Gly Ala Ala Leu Ala Ala Arg Leu His Val Ser Ala Pro 245 250 255 Ile Ala Met Val Val Ala Gly Leu Ile Ile Gly Asn His Gly Arg His 260 265 270 Tyr Ala Met Ser Asp Glu Thr Arg Arg Tyr Val Asp Lys Phe Trp Glu 275 280 285 Leu Ile Asp Glu Ile Leu Asn Ala Leu Leu Phe Ala Leu Ile Gly Leu 290 295 300 Glu Leu Leu Leu Leu Pro Phe Ser Trp Leu His Val Ala Ala Ala Phe 305 310 315 320 Ala Leu Gly Gly Ala Val Leu Val Ser Arg Leu Leu Thr Val Gly Pro 325 330 335 Ala Ile Leu Val Leu Arg Arg Phe Arg Gly Ala Asn Arg Gln Val Pro 340 345 350 Ala Gly Thr Ile Arg Ile Leu Val Trp Gly Gly Leu Arg Gly Gly Val 355 360 365 Ser Val Ala Leu Ala Leu Ser Leu Pro Leu Gly Pro Glu Arg Asp Leu 370 375 380 Ile Leu Ser Leu Thr Tyr Ile Val Val Leu Val Ser Ile Leu Leu Gln 385 390 395 400 Gly Leu Ser Ile Gly Pro Leu Val Arg Arg Ile Tyr Ala Gly Gln Pro 405 410 415 Leu Glu Lys Ser Glu Gly Ala His 420 5 20 DNA Artificial Sequence Synthetic DNA 5 ggatgatgat cgattcggat 20 6 20 DNA Artificial Sequence Synthetic DNA 6 atctgactca taggatatcg 20 7 20 DNA Artificial Sequence Synthetic DNA 7 ccttcacatc caaaacccac 20 8 20 DNA Artificial Sequence Synthetic DNA 8 gcacataccc acaaccagaa 20 9 23 DNA Artificial Sequence Synthetic DNA 9 gaatgttttg aaggatatct cag 23 10 21 DNA Artificial Sequence Synthetic DNA 10 gaaaaatgga gcacgaaatg c 21 11 20 DNA Artificial Sequence Synthetic DNA 11 cccgagatta atacacaatc 20 12 21 DNA Artificial Sequence Synthetic DNA 12 gcagattatg taattgtgac c 21 13 20 DNA Artificial Sequence Synthetic DNA 13 tcgtgtttac cgggtcggat 20 14 20 DNA Artificial Sequence Synthetic DNA 14 tgatgagaat cttagcgagc 20 15 21 DNA Artificial Sequence Synthetic DNA 15 tggtaagacc aaattacact c 21 16 23 DNA Artificial Sequence Synthetic DNA 16 cgtaattaaa atgtgttaaa ccg 23 17 20 DNA Artificial Sequence Synthetic DNA 17 aaccgcatag tacaatgcag 20 18 22 DNA Artificial Sequence Synthetic DNA 18 cggtaaagat caactaataa cg 22 19 20 DNA Artificial Sequence Synthetic DNA 19 aacggaaacg gcaactagac 20 20 20 DNA Artificial Sequence Synthetic DNA 20 accctaaatg tttcgattcg 20 

1. An isolated polynucleotide which encodes a protein comprising the amino acid sequence of SEQ ID NO:2.
 2. The isolated polynucleotide of claim 1, wherein said protein has Na⁺/H⁺ transporter activity.
 3. An isolated polynucleotide, which comprises SEQ ID NO:1.
 4. An isolated polynucleotide which is complimentary to the polynucleotide of claim
 3. 5. An isolated polynucleotide which is at least 70% identical to the polynucleotide of claim
 3. 6. An isolated polynucleotide which is at least 80% identical to the polynucleotide of claim
 3. 7. An isolated polynucleotide which is at least 90% identical to the polynucleotide of claim
 3. 8. An isolated polynucleotide which hybridizes under stringent conditions to the polynucleotide of claim 3; wherein said stringent conditions comprise washing in 5×SSC at a temperature from 50 to 68° C.
 9. The isolated polynucleotide of claim 3, which encodes a protein having Na⁺/H⁺ transporter activity.
 10. A vector comprising the isolated polynucleotide of claim
 1. 11. A vector comprising the isolated polynucleotide of claim
 3. 12. A host cell comprising the isolated polynucleotide of claim
 1. 13. A host cell comprising the isolated polynucleotide of claim
 3. 14. A plant cell comprising the isolated polynucleotide of claim
 1. 15. A plant cell comprising the isolated polynucleotide of claim
 3. 16. A transgenic plant comprising the isolated polynucleotide sequence of claim
 1. 17. A transgenic plant comprising the isolated polynucleotide sequence of claim
 3. 18. The transgenic plant of claim 16, wherein said plant is Arabidopsis thalania.
 19. The transgenic plant of claim 17, wherein said plaint is Arabidopsis thalania.
 20. The transgenic plant of claim 16, wherein said plant is selected from the group consisting of wheat, corn, peanut cotton, oat, and soybean plant.
 21. The transgenic plant of claim 16, wherein the isolated polynucleotide is operably linked to an inducible promoter.
 22. The transgenic plant of claim 17, wherein the isolated polynucleotide is operably linked to an inducible promoter.
 23. A process for screening for polynucleotides which encode a protein having Na⁺/H⁺ transporter activity comprising hybridizing the isolated polynucleotide of claim 1 to the polynucleotide to be screened; expressing the polynucleotide to produce a protein; and detecting the presence or absence of Na⁺/H⁺ transporter activity in said protein.
 24. A process for screening for polynucleotides which encode a protein having Na⁺/H⁺ transporter activity comprising hybridizing the isolated polynucleotide of claim 3 to the polynucleotide to be screened; expressing the polynucleotide to produce a protein; and detecting the presence or absence of Na⁺/H⁺ transporter activity in said protein.
 25. A process for screening for polynucleotides which encode a protein having Na⁺/H⁺ transporter activity comprising hybridizing the isolated polynucleotide of claim 8 to the polynucleotide to be screened; expressing the polynucleotide to produce a protein; and detecting the presence or absence of Na⁺/H⁺ transporter activity in said protein.
 26. A method for detecting a nucleic acid with at least 70% homology to nucleotide of claim 1, comprising contacting a nucleic acid sample with a probe or primer comprising at least 15 consecutive nucleotides of the nucleotide sequence of claim 1, or at least 15 consecutive nucleotides of the complement thereof.
 27. A method for producing a nucleic acid with at least 70% homology to nucleotide of claim 1, comprising contacting a nucleic acid sample with a primer comprising at least 15 consecutive nucleotides of the nucleotide sequence of claim 1, or at least 15 consecutive nucleotides of the complement thereof.
 28. A method for detecting a nucleic acid with at least 70% homology to nucleotide of claim 3, comprising contacting a nucleic acid sample-with a probe or primer comprising at least 15 consecutive nucleotides of the nucleotide sequence of claim 3, or at least 15 consecutive nucleotides of the complement thereof.
 29. A method for producing a nucleic acid with at least 70% homology to nucleotide of claim 3, comprising contacting a nucleic acid sample with a primer comprising at least 15 consecutive nucleotides of the nucleotide sequence of claim 3, or at least 15 consecutive nucleotides of the complement thereof.
 30. A method for making SOS1 protein, comprising culturing the host cell of claim 12 for a time and under conditions suitable for expression of SOS1, and collecting the SOS1 protein.
 31. A method for making SOS1, comprising culturing the host cell of claim 13 for a time and under conditions suitable for expression of SOS1, and collecting the SOS1 protein.
 32. A method of making a transgenic plant comprising introducing the polynucleotide of claim 1 to the plant.
 33. A method of making a transgenic plant comprising introducing the polynucleotide of claim 1 to the plant.
 34. A method of increasing the salt tolerance of a plant in need thereof, comprising introducing the polynucleotide of claim 1 to said plant.
 35. A method of increasing the salt tolerance of a plant in need thereof, comprising introducing the polynucleotide of claim 1 to said plant.
 36. A method of increasing the salt tolerance of a plant in need thereof, comprising enhancing the expression of the SOS1 gene in said plant.
 37. An isolated polypeptide comprising the amino acid sequence in SEQ ID NO:2.
 38. The isolated polypeptide of claim 37, which has Na+/H+ transporter activity.
 39. An isolated polypeptide which is at least 70% identical to the isolated polypeptide of claim 37 and which has Na+/H+ transporter activity.
 40. An isolated polypeptide which is at least 80% identical to the isolated polypeptide of claim 37 and which has Na+/H+ transporter activity.
 41. An isolated polypeptide which is at least 90% identical to the isolated polypeptide of claim 37 and which has Na+/H+ transporter activity.
 42. A isolated polypeptide which is at least 95% identical to the isolated polypeptide of claim 37 and which has Na+/H+ transporter activity. 